Liquefaction of natural gas by liquid nitrogen in a dual-compartmented dewar

ABSTRACT

A method and apparatus for on-site liquefaction of natural gas. The liquefaction apparatus comprises a Dewar having upper and lower inner chambers separated by a common heat exchange bulkhead. Liquid nitrogen is stored in the upper inner chamber, and precooled natural gas, supplied from a commercial line, is introduced into the top of the lower chamber. Heat loss to the natural gas in the upper chamber through the bulkhead causes liquefaction of the natural gas. Natural gas so liquefied may be supplied to a Dewar storage tank on a vehicle employing such LNG fuel.

United States Patent Grenci LIQUEFACTION OF NATURAL GAS BY LIQUID NITROGEN IN A DUAL-COMPARTMENTED DEWAR FOREIGN PATENTS OR APPLICATIONS 4l7,572 9/l925 Germany 62/40 OTHER PUBLICATIONS [76] Inventor: Carl A. Grenci, 479i Lesa Pl.,

Yorba Linda Cant 92686 R. B. Scott. Cryogenic Engmeermg, March 1959, Van Nostrand pp. 64-67. v Flledl 4, 1972 M. McClintock, Cryogenics, July 1965, Reinhold, pp. 211 App]. No.1 309,155 4849- Related Application Data Primary E.\'aminerN0rman Yudkoff [63] Continuation of Ser. No. 58.262. July 27, 1970. Assistant Ex min r-Frank Sever abandoned. Attorney, Agent, or Firm-Philip M. Hinderstein [52] US. Cl. 62/9; 62/36; 62/42 [57] ABSTRACT A method and apparatus for on site liquefaction of [58] Fleld of Search 62/9, 11, 40. 36, 50-54 namra] gas The li f ti apparatus comprises a Dewar having upper and lower inner chambers sepal References Clted rated by a common heat exchange bulkhead. Liquid UNITED STATES PATENTS nitrogen is stored in the upper inner chamber, and 1,917,154 7 1933 Porter 62/50 Precooled natural pp from a Commercial 19514 7 4/1934 Dana I I ,2/5 line, is introduced into the top of the lower chamber. 2,046,554 7/1936 Gay 62/54 Heat loss to the natural gas in the upper chamber 2,463,098 3/1949 G0ddard.... 62/52 through the bulkhead causes liquefaction of the natu- 2,928.254 3/1960 RHC 62/54 ra] gas Natural gas so liquefied may be upplied to 3 2,944,405 7/1960 Basorc 62/54 Dewar Storage tank a vehide employing Such LNG 3,282,059 ll/l966 Maher 62/40 fuel 3,400,547 9/1968 Williams.... 62/9 3,565,201 2/l97l Petsinger .1 62/52 12 Claims, 1 Drawing Figure all 1:- 1 i0 1 #7 Ir 1! :4

, 4! :1! g i: J

4I6'0EP770A/ m:

LIQLEFACTION OF NATURAL GAS BY LlQL'lD NITROGEN IN A DUAL-COMPARTMENTED DEWAR CROSS-REFERENCE TO RELATED APPLlCATlON This application is a continuation of my copending US. Pat. application Ser. No. 58.262. filed July 27. 1970 now abandoned for A System for Liquefaction of Natural Gas and Use of Same as a Vehicle Fuel.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for natural gas liquefaction for utilization of such liquefied natural gas as a vehicle fuel. More particularly. the invention relates to a method and apparatus whereby natural gas may be liquefied by thermal contact through a heat exchange bulkhead with liquid nitrogen.

2. Description of the Prior Art ln recent years. the problem of smog caused by automotive vehicle emissions has become acute. Such emissions typically comprise unburned hydrocarbons. carbon monoxide and other byproducts resulting from incomplete combustion of gasoline in conventional automobile engines.

While various solutions to the smog problem have been suggested. implementation of such approaches is impractical or uneconomical. For example. the use of steam or electric engines in vehicles may eliminate smog. but it would require many years to replace all existing conventional engines. Detergents or other additives in gasoline. or the utilization of catalytic mufflers or afterburners to achieve complete combustion or oxidation of engine emission components. are alternative approaches which treat the symptoms and not the cause of the emission problem.

A far more satisfactory approach to reduction of undesired automotive vehicle emissions is to use natural gas (substantially methane. CH.) as a fuel. Most conventional automotive engines now on the road can operate satisfactorily on natural gas fuel with only minor retuning or engine adjustment. Since almost complete combustion of the natural gas occurs in an engine. the vehicle exhaust is substantially free of unburned hydrocarbons and other smog-producing emissions.

In the past. only limited use has been made of natural gas as a vehicle fuel. Generally. the natural gas has been stored under very high pressure in a compressed gas cylinder mounted on the vehicle. Such compressed gas cylinders are of limited capacity. and typically restrict the range of the vehicle to approximately 90 miles. Moreover. expensive recharging equipment is necessary to refill such compressed gas cylinders. This makes it impractical to provide such gas recharging equipment at every neighborhood service station. A more satisfactory approach is to store the natural gas in liquid form on the vehicle. Such use ofliquid natural gas (LNG) would permit fuel sufficient for a vehicle range of 250 to 300 miles to be stored in a tank of relatively small volume. In the past. however. distribution of liquid natural gas to neighborhood service stations has been impractical.

It has been suggested that liquid natural gas could be produced at a central liquefaction facility. and then distributed by tank truck to neighborhood service stations. However. there are serious difficulties inherent in transporting liquid natural gas. Logistics of hauling tankers of LNG through populated areas and unloading same at neighborhood service stations pose many problems. one of which is safety. The proposed system will utilize existing liquid nitrogen distribution equipment with no special training required for delivery drivers. The safety of liquid nitrogen distribution is inherent to its inert physical characteristics.

These and other shortcomings of the prior art are overcome by using the present natural gas liquefaction system. The system envisions the on-site liquefaction at neighborhood service stations of natural gas supplied by commercial lines. To this end. there is disclosed a method and apparatus consuming liquid nitrogen which can be produced cheaply at a central facility and delivered easily with existing equipment to the service station. Let it be noted that plentiful supplies of liquid nitrogen are available in areas of high automotive air pollution. LNG produced at the service station is delivered to a low pressure Dewar storage tank on the automobile or other vehicle. The LNG powers the vehicle engine. permitting a range of several hundred miles with a tank of reasonable size.

SUMMARY OF THE INVENTION In accordance with the present invention. there is provided a method and apparatus for natural gas liquefaction. The apparatus typically may be situated at a neighborhood service station for on-site liquefaction of natural gas supplied via a commercial pipe line or main. Liquid natural gas may be delivered directly from the liquefaction apparatus to a vehicle equipped with-a Dewar tank for storage of the fuel.

In a preferred embodiment. the present liquefaction apparatus comprises a Dewar having a single outer wall and upper and lower inner chambers spaced from the wall and separated from each other by a common heat exchange bulkhead. The heat exchange bulkhead has a surface area which includes the bottom only of the upper chamber and the top only of the lower chamber so as to permit good heat transfer therebetween. The upper chamber is provided with a liquid inlet line and a gas outlet line whereas the lower chamber is provided with a gas inlet line to the top thereof and a liquid outlet line.

According to the present method. liquid nitrogen. or other liquid having a boiling point below that of natural gas. is introduced into the upper chamber. Typically. this liquid nitrogen may be delivered to the service station by tank truck from a central nitrogen liquefaction plant. Natural gas. supplied from a commercial pipe line. is introduced into the top of the lower chamber of the Dewar whereby only the gaseous natural gas in the top of the lower chamber comes into heat exchange contact with the bulkhead. Heat loss through the heat exchange bulkhead into the liquid nitrogen in the upper chamber results in liquefaction of the natural gas. partially filling the lower chamber with LNG. The natural gas may be precooled prior to introduction into the liquefaction Dewar by use of a gas-type refrigerator powered from the same commercial pipe line. Natural gas entering the liquefaction Dewar also may be precooled by means of heat exchangers communicating between the liquid nitrogen vent line and the natural gas supply line.

A two-conduit LNG delivery scheme may be used. with one line carrying LNG from the liquefaction Dewar to the vehicle Dewar storage tank. a second line venting the vehicle tank back to the vent space in the lower chamber of the liquefaction Dewar.

Thus it is an object of the present invention to provide a natural gas liquefaction system.

Another object of the present invention is to provide a novel. simple method and apparatus for liquefaction of natural gas or the like.

It is another object of the present invention to provide liquefaction apparatus and a method utilizing such apparatus comprising a Dewar having upper and lower inner chambers communicating through a common heat exchange bulkhead. gas introduced into the lower chamber being liquified as a result of heat loss through the bulkhead to a cryogenic liquid stored in the upper chamber.

Still another object of the present invention is to provide natural gas liquefaction apparatus comprising means for precooling natural gas. and a doublechambered Dewar for liquefaction of the precooled natural gas introduced into one chamber by heat exchange to the other chamber.

BRIEF DESCRIPTION OF THE DRAWINGS Still other objects. features. and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of the preferred embodiment constructed in accordance therewith. taken in conjunction with the accompanying drawings wherein:

The sole FIGURE is a diagrammatic view of natural gas liquefaction apparatus constructed in accordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings. there is shown a natural gas liquefaction apparatus in accordance with the present invention. Apparatus 10 receives natural gas from a commercial pipe line or main l1 and liquefies the same in a double-chambered Dewar 12 to produce liquid natural gas (LNG) 13. Natural gas so liquefied may be supplied via a delivery line 14 to a vehicle using LNG as a fuel. Alternatively. LNG produced by apparatus 10 may be used for any other application.

Liquefaction Dewar 12 comprises a single outer wall 15. typically fabricated of stainless steel and being generally cylindrical with a domed top 16 and bottom 17.

Disposed within outer wall 15, and separated therefrom by a vacuum space 18. are vertically spaced inner chambers 19 and 20 separated by a common heat exchange bulkhead 21. Upper inner chamber 19 may be generally cylindrical with a domed top 19. Similarly. lower inner chamber 20 may be cylindrical with a domed bottom 20'. Heat exchange bulkhead 21, which forms the bottom only of upper chamber 19 and the top only of lower chamber 20. may be domed in configuration. Alternatively. barrier 21 may be provided with fins (not shown) or otherwise configured to increase the surface area exposed to the interiors of chambers 19 and 20. In any event. bulkhead 21 has a surface area which permits good heat transfer between the bottom of upper chamber 19 and the top of lower chamber 21. bulkhead 21 providing the only communication between chambers 19 and 20. there being no liquid communication therebetween.

Upper inner chamber 19 may be filled with a cryogenic liquid having a boiling point lower than that of the gas to be liquefied. Thus. to liquefy natural gas. which has a boiling point on the order of 260 F.. chamber 19 may be filled with liquid nitrogen (LN:) 25 having a boiling point on the order of 320 F.

To facilitate filling of chamber 19. liquefaction Dewar 12 is provided with an inlet line 26 which passes through a pair of fittings 27 and 28 situated respectively in the wall of chamber 19 and in outer wall 15. Inlet line 26 communicates via a pair of valves 29 and 30 to an LN: delivery line 31. For improved thermal insulation. and to facilitate external connection adjacent the bottom of Dewar 12.. a portion 26' of inlet line 26 extends through vacuum space 18. Such configuration minimizes evaporation of LNg being introduced into inner chamber 19. Similar treatment can be given line 32.

Chamber 19 may be filled from the bottom thereof by opening valves 29 and 30. Alternatively. upper chamber 19 may be filled from the top via another inlet line 32 communicating with LNg delivery line 31 via valve 30 and another valve 33. Thus. if the nitrogen chamber pressure is high. valve 29 may be closed. valves 30 and 33 opened. and the colder nitrogen supplied via inlet 32 to the top of chamber 19. The colder nitrogen will recondense to fill chamber 19 with LN Line 32 also serves as a vent line for upper chamber 19. and accordingly is connected via a line 34 and a relief valve 35 to a vent outlet line 36. Line 43 also is connected via a valve 37 to a blow-down outlet 38. Further. vent line 34 is connected via a pair of heat exchangers 41 and 42. the function of which will be described below. and via a back pressure regulator 43 and valve 44 to a gaseous nitrogen vent outlet 45.

In order to introduce natural gas into lower chamber 20. liquefaction Dewar 12 is provided with an inlet line 48 which passes through a pair of fittings in the wall of chamber 20 and in outer wall 15. Inlet line 48 passes into lower chamber 20 without contacting upper chamber 19 and terminates adjacent bulkhead 21. in the top of chamber 20. The reason for this is that natural gas has a freezing point which is higher than the boiling point of liquid nitrogen and contact between line 48 and chamber 19 would result in freezing of the gas in line 48.

Natural gas inlet 48 communicates with a supply line 49 which is connected via a relief valve 50 to a relief outlet 51. Further. supply line 49 receives natural gas precooled in heat exchangers 41 and 42 and in another heat exchanger 52 associated with a Servel absorption-type refrigeration unit 53. In this regard. natural gas supply line 11 communicates with heat exchangers 41. 42. and 52. and thence with line 49 to liquefaction Dewar 12. via an inlet valve 54 and one of a pair of gas purifier batteries 55a and 55b and the associated valves 56a. 56b. 57a. and 5712. Supply line 49 also is connected back to natural gas line 11 via a heater 60 and a back pressure regulator 61. Heater 60 also may be connected via a valve 46 to an outlet 47 used for venting from chamber 20 non-condensible vapors such as helium or nitrogen which may be present in the natural gas.

Liquid natural gas 13 produced in liquefaction Dewar 12 may be delivered therefrom via a pump 62 situated either within or adjacent to the bottom of lower chamber 20. Pump 62 is connected via a valve 63 and delivery line 14 to an appropriate fitting 64 functioning as a fill and vent return connection. Fitting 64 also is connected via a vent return line 65. a valve 66. and heat exchanger 41 to vent line 49.

Operation of liquefaction apparatus now will be described. lnitially. valves 33. 37. 54. 63. and 66 all are closed. Liquid nitrogen (or other cryogenic liquid having a boiling point lower than that of the gas to be liquefled) isintroduced into Dewar upper chamber 19 via fill line 31. open valves 29 and 30. and inlet line 26. By way of example. liquid nitrogen may be used. this being supplied via tank truck from a centralnitrogen liquefaction plant.

The nitrogen vapor pressure in vapor space 67 within chamber 19 above liquid may be controlled by the setting of relief valve and/or by the setting of back pressure regulator 43. This vapor pressure in turn will determine the temperature of liquid nitrogen 25. When upper chamber 19 has been substantially filled. valves 29 and 30 are closed. Heat leakage into chamber 19 will cause some evaporation of liquid nitrogen 25. the resultant cold nitrogen vapor being vented via outlet 32. line 34. heat exchangers 41 and 42. back pressure regulator 43. open valve 44. and vent outlet 45. As presently will be described. this vent vapor aids in precooling natural gas supplied to liquefaction Dewar 12.

Next. valve 54 and valves 56a and 57a (alternatively 56b and 57b) are opened to permit natural gas from commercial supply line 11 to flow to liquefaction Dewar 12. In particular. the supplied natural gas is cleansed of CO water. and other impurities by gas purifier battery 55a (or 5512). For this purpose. purifiers 55a and 55b may comprise molecular sieves. one of which is being regenerated while the other is in use.

The purified natural gas next is precooled successively in heat exchangers 42. 52. and 41. As noted earlier. heat exchanger 52 is associated with an absorption-type refrigeration unit 53 which itself may utilize as an energy source natural gas supplied from line 11. Typically. refrigeration unit 53 and heat exchanger 52 will cool the purified natural gas down to a temperature on the order of from about zero to about -l0 F. At the initiation of liquefaction within Dewar 12. precooling of natural gas supplied from line 11 primarily will be accomplished by refrigeration unit 53 and heat exchanger 52.

The precooled natural gas next is introduced into the top of Dewar lower chamber 20 via supply line 49 and inlet 48. This precooled natural gas then comes in contact with heat exchange bulkhead 21. which bulkhead itself is in thermal contact with. and hence at substantially the same temperature as. liquid nitrogen 25 in upper chamber 19. Accordingly. the natural gas is cooled to below its boiling point. causing immediate liquefaction of the natural gas. Alternatively expressed. heat from the natural gas introduced into chamber 20 via inlet 48 is communicated via heat exchange bulkhead 21 into the liquid nitrogen 25 in upper chamber 19. The resultant heat loss causes liquefaction of the natural gas. thereby accumulating liquid natural gas 13 within lower chamber 20.

As liquefaction continues. heat loss from the natural gas through heat exchange bulkhead 21 will cause gradual evaporation of liquid nitrogen 25 in upper chamber 19. Accordingly. the pressure in vapor space 67 will tend to increase and additional nitrogen vapor will be vented via outlet 32, line 34, heat exchangers 41 and 42. and vent outlet 45. This flow of nitrogen vapor. which is considerably colder than the temperature of the natural gas supplied from line 11. will cause precooling of the natural gas through operation of heat exchangers 41 and 42. This in turn will reduce the temperature of the natural gas introduced into Dewar 12 via inlet 48. Accordingly. less heat will be exchanged into liquid nitrogen 25. and the rate of evaporation thereof will be reduced. This will conserve the heat sink provided by liquid nitrogen 25.

Gradually. an equilibrium situation may be reached at which a minimum amount of liquid nitrogen may be consumed during liquefaction of a unit volume of natural gas. In this regard. back pressure regulator 43 may be used to keep the vapor pressure within upper chamber 19 at a most efficient value. Typically. this vapor pressure may be on the order of psi. at which pressure liquid nitrogen 25 may be about l0 to 15 F. below the gas liquefaction temperature.

When sufficient liquid natural gas 13 has been accumulated within lower chamber 20. valve 54 may be closed to terminate the liquefaction operation. Alternatively. if LNG is withdrawn periodically or continuously from Dewar 12. valve 54 may be opened to permit continuous or periodic liquefaction of additional natural gas. or this may be done by automatic controls.

lf LNG 13 is stored within Dewar 12 for an extended duration of time without LN- in chamber 19. heat leakage into Dewar 12 may result in evaporation of some of the stored LNG. As a result. the vapor pressure in the vapor space 68 at the top of lower chamber 20 may exceed a desired level determined by the setting of back pressure regulator 61. In this instance. the excess natural gas vapor will be vented through inlet 48. warmed by heater 60. and supplied back into the natural gas supply line 11. As a result. no natural gas will be lost to the atmosphere. Note that heater heats the natural gas vapors to a temperature sufficiently high (typically 0 F. or above) so that the cold gas will not cause fracture of the carbon steel pipe typically used in natural gas pipe line 11.

To deliver liquid natural gas 13 to a user. valves 63 and 66 both are opened. and vent-fill connection 64 is attached to the users storage Dewar. In particular. delivery line 14 is connected to the interior of the storage Dewar and vent return line 65 is connected to the vent space of the same storage Dewar. Thus a closed system is achieved. with the vent space of the storage Dewar being connected back via vent return line 65. supply line 49. and inlet 48 to vapor space 68 of liquid nitrogen chamber 20. Any vent vapor returned via line 65 will be precooled by heat exchanger 41 before entry to chamber 20. Pump 62 then may be used to facilitate delivery of LNG 13 via line 14 to the storage Dewar; however. for some applications. pump 62 may not be required. When filling is complete. valves 63 and 66 are closed. and fitting 64 disconnected.

Apparatus 10 thus provides a simple system for onsite liquefaction of natural gas. The apparatus is relatively low in cost. and is particularly well suited for installation and utilization at a neighborhood service station. In such installation. natural gas may be supplied via a commercial pipe line. while liquid nitrogen can be delivered by tank truck safely from a central LN- liquefaction facility. Apparatus 10 thus can facilitate wide' spread distribution of liquid natural gas for use as a vehicle fuel.

While the invention has been described with respect to a preferred physical embodiment constructed in accordance therewith. it will be apparent to those skilled in the art that various modifications and improvement may be made without departing from the scope and spirit of the invention. Accordingly. it is to be understood that the invention is not to be limited by the specific illustrative embodiment. but only by the scope of the appended claims.

I claim: I. A method for liquefaction of natural gas comprising the steps of:

providing a Dewar having an outer wall and upper and lower inner chambers separated by a common heat exchange bulkhead. said heat exchange bulkhead having a surface area which includes the bottom only of said upper chamber and the top only of said lower chamber and which is sufficient to permit good heat transfer therebetween. said bulkhead providing the only communication between said chambers. there being no liquid communication therebetween; introducing a cryogenic liquid having a boiling point lower than that of said natural gas into said upper chamber:

introducing said natural gas into the top of said lower chamber and into heat exchange contact with said bulkhead. heat loss to said cryogenic liquid in said upper chamber through said heat exchange bulkhead causing liquefaction of said natural gas in said lower chamber. said liquefied natural gas falling into the lower portion of said lower chamber. away from said bulkhead. to prevent further cooling thereof; and

delivering said liquefied natural gas from said lower chamber to a utilization device.

2. A method according to claim 1 wherein said cryogenic liquid comprises liquid nitrogen.

3. A method according to claim 1 wherein said cryogenic liquid confined in said upper chamber and only the gaseous natural gas confined in said top of said lower chamber are in contact with opposite sides of said heat exchange bulkhead. there being no contact between said bulkhead and said liquefied natural gas.

4. A method according to claim 3 further comprising the steps of:

providing a vent line from the top of said upper chamber; and

conducting said natural gas into heat exchange relationship with said vent line from said upper chamber to precool said natural gas before introducing said natural gas into said lower chamber.

5. A method according to claim 1 wherein said step of introducing said natural gas into the top of said lower chamber comprises the step of:

conducting said natural gas through said outer wall of said Dewar and into said lower chamber without contacting said upper chamber to prevent freezing of said natural gas.

6. A method according to claim 1 wherein said step of delivering said liquefied natural gas from said lower chamber comprises the step of:

conducting said liquefied natural gas from said lower chamber through said outer wall of said Dewar without contacting said upper chamber to prevent further cooling of said liquefied natural gas.

7. Apparatus for liquefaction of natural gas comprising:

a Dewar having an outer wall and upper and lower inner chambers separated by a common heat exchange bulkhead. said heat exchange bulkhead having a surface area which includes the bottom only of said upper chamber and the top only of said lower chamber and which is sufficient to permit good heat transfer therebetween. said bulkhead providing the only communication between said chambers. there being no liquid communication therebetween;

means for introducing a cryogenic liquid having a boiling point lower than that of said natural gas into said upper chamber; 7

inlet means passing through the outer wall of said Dewar and into said lower chamber without contacting said upper chamber for introducing said natural gas to said top of said lower chamber. only said gaseous natural gas in said top of said lower chamber coming into heat exchange contact with said bulkhead. heat loss to said cryogenic liquid in said upper chamber through said heat exchange bulkhead causing liquefaction of said natural gas in said lower chamber; and

outlet means passing through said outer wall of said Dewar and into said lower chamber without contacting said upper chamber for delivering said liquefied natural gas from said lower chamber.

8. Apparatus as defined in claim 7-wherein said upper and lower inner chambers are spaced from said outer wall by an insulating space. liquid confined in said upper chamber and vapor confined it said lower chamber being in contact with opposite sides of said heat exchange bulkhead. there being no contact between said bulkhead and said liquefied natural gas confined in said lower chamber.

9. Apparatus as defined in claim 7 wherein said means for introducing said natural gas comprises a supply line to the vapor space at the top of said lower chamber and means for precooling gaseous natural gas in said supply line.

10. Apparatus as defined in claim 9 further comprising a vent line from said upper chamber. and wherein said means for precooling comprises heat exchange means communicating between said vent line and said supply line. I

11. Apparatus as defined in claim 9 wherein said means for precooling comprises gas refrigeration means connected to said supply line.

12. Apparatus as defined in claim 7 wherein said means for delivering comprises a delivery line carrying liquefied natural gas from said lower chamber and a vent return line communicating with the vapor space at said top of said lower chamber. 

1. A METHOD FOR LIQUEFACTION OF NATURAL GAS COMPRISING THE STEPS OF: PROVIDING A DEWAR HAVING AN OUTER WALL AND UPPER AND LOWER INNER CHAMBERS SEPARATED BY A COMMON HEAT EXCHANGE BULKHEAD, SAID HEAT EXCHANGE BULKHEAD HAVING A SURFACE AREA WHICH INCLUDES THE BOTTOM ONLY OF SAID UPPER CHAMBER AND THE TOP ONLY OF SAID LOWE CHAMBER AND WHICH SUFFICIENT TO PERMIT GOOD HEAT TRANSFER THEREBETWEEN, SAID BULKHEAD, PROVIDING THE ONLY COMMUNICATION BETWEEN SAID CHAMBERS, THERE BEING NO LIQUID COMMUNICATION THEREBETWEEN; INTRODUCING A CRYOGENIC LIQUID HAVING A BOILING POINT LOWER THAN THAT OF SAID NATURAL GAS INTO SAID UPPER CHAMBER; INTRODUCING SAID NATURAL GAS INTO THE TOP OF SAID LOWER CHAMBER AND INTO HEAT EXCHANGE CONTACT WITH SAID BULKHEAD, HEAT LOSS TO SAID CRYOGENIC LIQUID IN SAID UPPER CHAMBER THROUGH SAID HEAT EXCHANGE BULKHEAD CAUSING LIQUEFACTION OF SAID NATURAL GAS IN SAID LOWER CHAMBER, SAID LIQUEFIED NATURAL GAS FALLING INTO THE LOWER PORTION OF SAID LOWER CHAMBER, AWAY FROM SAID BULKHEAD, TO PREVENT FURTHER COOLING THEREOF; AND DELIVERING SAID LIQUEDIED NATURAL GAS FROM SAID LOWER CHAMBER TO A UTILIZATION DEVICE.
 1. A method for liquefaction of natural gas comprising the steps of: providing a Dewar having an outer wall and upper and lower inner chambers separated by a common heat exchange bulkhead, said heat exchange bulkhead having a surface area which includes the bottom only of said upper chamber and the top only of said lower chamber and which is sufficient to permit good heat transfer therebetween, said bulkhead providing the only communication between said chambers, there being no liquid communication therebetween; introducing a cryogenic liquid having a boiling point lower than that of said natural gas into said upper chamber; introducing said natural gas into the top of said lower chamber and into heat exchange contact with said bulkhead, heat loss to said cryogenic liquid in said upper chamber through said heat exchange bulkhead causing liquefaction of said natural gas in said lower chamber, said liquefied natural gas falling into the lower portion of said lower chamber, away from said bulkhead, to prevent further cooling thereof; and delivering said liquefied natural gas from said lower chamber to a utilization device.
 2. A method according to claim 1 wherein said cryogenic liquid comprises liquid nitrogen.
 3. A method according to claim 1 wherein said cryogenic liquid confined in said upper chamber and only the gaseous natural gas confined in said top of said lower chamber are in contact with opposiTe sides of said heat exchange bulkhead, there being no contact between said bulkhead and said liquefied natural gas.
 4. A method according to claim 3 further comprising the steps of: providing a vent line from the top of said upper chamber; and conducting said natural gas into heat exchange relationship with said vent line from said upper chamber to precool said natural gas before introducing said natural gas into said lower chamber.
 5. A method according to claim 1 wherein said step of introducing said natural gas into the top of said lower chamber comprises the step of: conducting said natural gas through said outer wall of said Dewar and into said lower chamber without contacting said upper chamber to prevent freezing of said natural gas.
 6. A method according to claim 1 wherein said step of delivering said liquefied natural gas from said lower chamber comprises the step of: conducting said liquefied natural gas from said lower chamber through said outer wall of said Dewar without contacting said upper chamber to prevent further cooling of said liquefied natural gas.
 7. Apparatus for liquefaction of natural gas comprising: a Dewar having an outer wall and upper and lower inner chambers separated by a common heat exchange bulkhead, said heat exchange bulkhead having a surface area which includes the bottom only of said upper chamber and the top only of said lower chamber and which is sufficient to permit good heat transfer therebetween, said bulkhead providing the only communication between said chambers, there being no liquid communication therebetween; means for introducing a cryogenic liquid having a boiling point lower than that of said natural gas into said upper chamber; inlet means passing through the outer wall of said Dewar and into said lower chamber without contacting said upper chamber for introducing said natural gas to said top of said lower chamber, only said gaseous natural gas in said top of said lower chamber coming into heat exchange contact with said bulkhead, heat loss to said cryogenic liquid in said upper chamber through said heat exchange bulkhead causing liquefaction of said natural gas in said lower chamber; and outlet means passing through said outer wall of said Dewar and into said lower chamber without contacting said upper chamber for delivering said liquefied natural gas from said lower chamber.
 8. Apparatus as defined in claim 7 wherein said upper and lower inner chambers are spaced from said outer wall by an insulating space, liquid confined in said upper chamber and vapor confined n said lower chamber being in contact with opposite sides of said heat exchange bulkhead, there being no contact between said bulkhead and said liquefied natural gas confined in said lower chamber.
 9. Apparatus as defined in claim 7 wherein said means for introducing said natural gas comprises a supply line to the vapor space at the top of said lower chamber and means for precooling gaseous natural gas in said supply line.
 10. Apparatus as defined in claim 9 further comprising a vent line from said upper chamber, and wherein said means for precooling comprises heat exchange means communicating between said vent line and said supply line.
 11. Apparatus as defined in claim 9 wherein said means for precooling comprises gas refrigeration means connected to said supply line. 